Polypropylene is a widely used plastic that has high modulus, high tensile strength, good heat resistance, and other favorable properties in the sold-state. However, due to its linear molecular architecture, polypropylene generally has relatively poor melt strength, which negatively affects its processability while in the molten state. Low melt strength limits polypropylene resins in a number of applications, such as foaming, sheet extrusion thermoforming, extrusion blow molding, extrusion coating, and the like.
The melt strength is generally increased by the addition of long-chain branches to the polymer structure. On the other hand, long chain branches bonded within the polymer structure can make the polymer too rigid, compromising the polymer's thermoplastic character. Thus, methods of making high melt strength polypropylene (HMS-PP) are needed to promote long chain branching without sacrificing the thermoplastic character.